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Mitral stenosis (MS) is narrowing of the mitral orifice that impedes blood flow from the left atrium to the left ventricle. The (almost) invariable cause is rheumatic fever. Common complications are pulmonary hypertension, atrial fibrillation, and thromboembolism. Symptoms are those of heart failure; signs include an opening snap and a diastolic murmur. Diagnosis is by physical examination and echocardiography. Prognosis is good. Medical treatment includes diuretics, β-blockers or rate-limiting Ca channel blockers, and anticoagulants. Effective treatment for more severe disease consists of balloon valvotomy, surgical commissurotomy, or valve replacement.
In MS, mitral valve leaflets become thickened and immobile and the mitral orifice becomes narrowed due to fusion of the commissures and the presence of shortened, thickened and matted chordae. The most common cause is rheumatic fever (see Rheumatic Fever), even though many patients do not recall the disorder. Very rare causes include mitral annular calcification, bacterial endocarditis, SLE, atrial myxoma, RA, malignant carcinoid syndrome with an atrial right-to-left shunt, and methysergide. Occasionally, MS is congenital. If the valve cannot close completely, mitral regurgitation (MR) may coexist with MS. Patients with MS due to rheumatic fever may also have lesions of the aortic or tricuspid valve or both.
Left atrial (LA) size and pressure increase progressively to compensate for MS; pulmonary venous and capillary pressures also increase and may cause secondary pulmonary hypertension, leading to right ventricular (RV) heart failure and tricuspid and pulmonic regurgitation. Rate of progression varies.
LA enlargement predisposes to atrial fibrillation (AF), a risk factor for thromboembolism. The faster heart rate and loss of atrial contraction with onset of AF often leads to sudden worsening of symptoms.
Symptoms and Signs
Symptoms correlate poorly with disease severity because the disease often progresses insidiously and patients reduce their activity without being aware of it. Many patients are asymptomatic until they become pregnant or AF develops. Initial symptoms are usually those of heart failure (eg, exertional dyspnea, orthopnea, paroxysmal nocturnal dyspnea, fatigue). They typically do not appear until 15 to 40 yr after an episode of rheumatic fever, but in developing countries, much younger children may become symptomatic because streptococcal infections may not be treated with antibiotics and recurrent infections are common. Paroxysmal or chronic AF further reduces blood flow into the left ventricle (LV), precipitating pulmonary edema and acute dyspnea when ventricular rate is poorly controlled. AF may also cause palpitations; in up to 15% of patients not taking anticoagulants, it causes systemic embolism with symptoms of stroke or other organ ischemia.
Less common symptoms include hemoptysis due to rupture of small pulmonary vessels and pulmonary edema, particularly during pregnancy when blood volume increases; hoarseness due to compression of the left recurrent laryngeal nerve by a dilated LA or pulmonary artery (Ortner syndrome); and symptoms of pulmonary hypertension (see Pulmonary Hypertension: Symptoms and Signs) and RV failure (see Heart Failure: RV failure).
Inspection and palpation may detect palpable 1st and 2nd heart sounds (S1 and S2). S1 is best palpated at the apex, and S2 at the upper left sternal border. The pulmonic component of S2 (P2) is responsible for the impulse and results from pulmonary hypertension. An RV impulse (heave) palpable at the left sternal border may accompany jugular venous distention when pulmonary hypertension is present and RV diastolic dysfunction develops.
Auscultatory findings include a loud S1 caused by the leaflets of a stenotic mitral valve closing abruptly (M1); it is heard best at the apex. A normally split S2 with an exaggerated P2 due to pulmonary hypertension is also heard. Most prominent is an early diastolic opening snap as the leaflets billow into the LV, which is loudest close to left lower sternal border; it is followed by a low-pitched decrescendo-crescendo rumbling diastolic murmur, heard best with the bell of the stethoscope at the apex (or over the palpable apex beat) at end-expiration when the patient is in the left lateral decubitus position. The opening snap may be soft or absent if the mitral valve is calcified; the snap moves closer to S2 (increasing duration of the murmur) as MS becomes more severe and LA pressure increases. The diastolic murmur increases after a Valsalva maneuver (when blood pours into the LA), after exercise, and in response to maneuvers that increase afterload (eg, squatting, isometric handgrip). The murmur may be softer or absent when an enlarged RV displaces the LV posteriorly and when other disorders (pulmonary hypertension, right-sided valve abnormalities, AF with fast ventricular rate) decrease blood flow across the mitral valve. The presystolic crescendo is caused by increased flow with atrial contraction. However, the closing mitral valve leaflets during LV contraction may also contribute to this finding but only at the end of short diastoles when LA pressure is still high.
Diastolic murmurs that may coexist with the MS murmur are
MS may cause signs of cor pulmonale (see Heart Failure: Cor Pulmonale). The classic mitral facies, a plum-colored malar flush, occurs only when cardiac output is low and pulmonary hypertension is severe; cause is cutaneous vasodilation and chronic hypoxemia.
Occasionally, the initial symptoms and signs of MS are those of an embolic event such as stroke. Endocarditis is rare in MS unless MR is also present.
Diagnosis
Diagnosis is suspected clinically and confirmed by echocardiography. Typically, 2-dimensional echocardiography shows abnormal valve and subvalve structures. It also provides information about the degree of valvular calcification and stenosis and LA size. Doppler echocardiography provides information about the transvalvular gradient and pulmonary artery pressure. The normal area of the mitral valve orifice is 4 to 5 cm2. An area of 1 to 1.5 cm2 or mean transmitral gradient 5 to 10 mm Hg reflects moderate MS and often causes exertional symptoms. An area < 1 cm2 or mean gradient > 10 mm Hg represents severe stenosis and may cause symptoms during rest. However, the relationship between the area of the valve orifice and symptoms is not always consistent. Color Doppler echocardiography detects associated MR.Transesophageal echocardiography can be used to detect or exclude small LA thrombi, especially those in the LA appendage, which usually cannot be seen transthoracically.
An ECG and chest x-ray are usually obtained. The ECG may show LA enlargement, manifest as a P wave lasting > 0.12 msec with prominent negative deflection of its terminal component (duration: > 0.04 msec; amplitude: > 0.10 mV) in V1; broad, notched P waves in lead II; or both. Low voltage in V1, right axis QRS deviation, and tall R waves in V1 suggest RV hypertrophy.
Chest x-ray usually shows straightening of the left cardiac border due to a dilated LA appendage, and widening of the carina. With barium in the esophagus, the lateral chest x-ray will show the dilated LA displacing the esophagus posteriorly. The main pulmonary artery (trunk) may be prominent; the descending right pulmonary artery diameter is ≥ 16 mm if pulmonary hypertension is significant. The upper lobe pulmonary veins may be dilated. A double shadow of an enlarged LA may be seen along the right cardiac border. Horizontal lines in the lower posterior lung fields (Kerley B lines) indicate interstitial edema associated with high LA pressure.
Cardiac catheterization, indicated only for perioperative assessment of coronary artery disease (CAD) before surgical repair, can confirm elevated LA and pulmonary artery pressures, mitral gradient and valve area.
Prognosis
The natural history of MS varies, but the interval between onset of symptoms and severe disability is about 7 to 9 yr. Outcome is affected by the patient's preprocedural age and functional status, pulmonary hypertension, and degree of MR. Symptomatic results of balloon valvotomy and surgical commissurotomy are equivalent in patients with valves that are not calcified. However, after a variable period of time, function deteriorates in most patients due to restenosis, and valve replacement may become necessary. Risk factors for death are AF and pulmonary hypertension. Cause of death is most commonly heart failure or pulmonary or cerebrovascular embolism.
Treatment
Asymptomatic patients require no treatment other than appropriate prophylaxis against rheumatic fever recurrence.
Mildly symptomatic patients usually respond to diuretics and, if sinus tachycardia or AF is present, to β-blockers or Ca channel blockers, which can control ventricular rate. Anticoagulants are indicated to prevent thromboembolism if AF is present or in sinus rhythm if embolism occurs or a clot is present in the left atrium. Anticoagulation should also be considered in the presence of dense spontaneous contrast or an enlarged left atrium (M-mode diameter > 50 mm). All patients should be encouraged to continue at least low levels of physical exercise despite exertional dyspnea.
More severely symptomatic patients and patients with evidence of pulmonary hypertension require valvotomy, commissurotomy, or valve replacement.
Percutaneous balloon valvotomy (commissurotomy) is the procedure of choice for younger patients and for patients without heavily calcified valve commissures, subvalvular distortion, LA thrombi, or significant MR. In this fluoroscopic- and echocardiographic-guided procedure, a transvenous catheter with an inflatable distal balloon is passed transseptally from the right atrium to the LA and inflated to separate fused mitral valve commissures. Outcomes are equivalent to those of more invasive procedures. Complications are uncommon but include MR, embolism, and tamponade.
Patients with severe subvalvular disease, valvular calcification, or LA thrombi may be candidates for surgical commissurotomy, in which fused mitral valve leaflets are separated using a dilator passed through the LV (closed commissurotomy) via a thoracotomy, or by direct vision (open commissurotomy) via a sternotomy. Choice of procedure is based on surgeon's experience and the morphology of the valve, although closed valvotomy is now done less frequently in Western countries.
Valve replacement is confined to patients with severe morphologic changes that make the valve unsuitable for balloon or surgical valvotomy.
Antibiotic prophylaxis against endocarditis is no longer recommended except for patients who have had valve replacement (see Table 4: Endocarditis: Recommended Endocarditis Prophylaxis During Oral-Dental or Respiratory Tract Procedures* ).
Key Points
Last full review/revision November 2012 by Guy P. Armstrong
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